Make update_engine use /data/misc/update_engine/cache as tmpdir

update_engine doesn't have access to android's default tmpdir,
/data/local/tmp . So use /data/misc/update_engine/cache/

Test: th
Bug: 320443894
Change-Id: Ibbbe8019c276fe0fa3f9ea197815ed6daac912fc
diff --git a/common/utils.cc b/common/utils.cc
index f0c045f..1fa2d41 100644
--- a/common/utils.cc
+++ b/common/utils.cc
@@ -86,6 +86,7 @@
 // The path to the kernel's boot_id.
 const char kBootIdPath[] = "/proc/sys/kernel/random/boot_id";
 
+}  // namespace
 // If |path| is absolute, or explicit relative to the current working directory,
 // leaves it as is. Otherwise, uses the system's temp directory, as defined by
 // base::GetTempDir() and prepends it to |path|. On success stores the full
@@ -110,8 +111,6 @@
   return true;
 }
 
-}  // namespace
-
 namespace utils {
 
 bool WriteFile(const char* path, const void* data, size_t data_len) {